(1) Field of the Invention
The invention relates to a charge/discharge protection circuit for a rechargeable battery, and more particularly, to a circuit which is protected by a fuse, comprising a control circuit which opens or closes a load switch depending on the magnitude of the battery voltage, the voltage on the charge/discharge terminals of said protection circuit and the charge/discharge current.
(2) Description of the Prior Art
Charge/discharge protection circuits are particularly used in so called battery packs for mobile phones and monitor inter alia the maximum/minimum voltages of charging/discharging of said battery and the maximum allowable charge/discharge currents. In case of exceeding said limits said load switch is opened. One example of such a protection circuit is the U.S. application Ser. No. 10/057,490, filed on Jan. 24, 2002, herein incorporated by reference. Said protection circuit of U.S. application Ser. No. 10/057,490 can particularly be positioned between a single Lithium-Ion cell and the circuitry of a mobile phone.
All manufacturers of mobile phones offer battery chargers specific to their mobile phones and to the battery packs of said mobile phones. Nevertheless there are sometimes attempts to charge a battery using a battery charger produced by a different manufacturer. Subject of U.S. application Ser. No. 10/057,490 is a protection circuit which detects, inter alia, a charging voltage being too high produced e.g. by a defective battery charger or by a battery charger from a different manufacturer and reliably disconnects the battery to avoid a dangerous overcharging prior to a destruction of said protection circuit by said overvoltage. The protection circuit of said patent application admittedly can not differentiate between the occurrence of a short-time overvoltage and of a long-time overvoltage, thus it also disconnects the battery permanently from the charge/discharge terminals and as the case may be will be destructed even if said overvoltage is merely caused by a capacitor of a battery charger charged to an increased open circuit voltage.
The objective of the invention is to achieve a charge/discharge protection circuit of the above-described type but being able to differentiate between the occurrences of a short-time overvoltage on the charge/discharge terminals and between a long-time occurring overvoltage. In the first case the overvoltage has to be shunted reliably, in the second case the battery has to be disconnected permanently.
In accordance with the objects of this invention a charge/discharge protection circuit for a rechargeable battery has been achieved. Said circuit, secured by a fuse, is comprising a control circuit, which opens or closes a load switch, dependent on the magnitude of the voltage on the battery terminals, the voltage on the charge/discharge terminals of said protection circuit and on the magnitude of the charge/discharge current. Said circuit is characterized that a number of partial switches is located parallel to the load switch, that an overvoltage detector closes, in case of an overvoltage on charge/discharge terminals, all partial switches via a control logic, which afterwards cyclically progressing opens one partial switch after the other, and that a voltage detector, monitoring the remaining voltage over the partial switches inhibits the opening of at that time next partial switch if the remaining voltage over the still closed partial switches is higher than a predefined limit of said remaining voltage. Furthermore said circuit is characterized that the control logic activates a permanent disconnection of the battery from the charge/discharge terminals if the cycle is not completed within a predefined time Interval, that means, if at least the last partial switch is still closed.
Also in accordance with the objects of this invention a charge/discharge protection circuit for a rechargeable battery has been achieved. Said circuit, secured by a fuse, comprises a control circuit, which opens or closes a load switch, dependent on the magnitude of the voltage on the battery terminals, the voltage on the charge/discharge terminals of said protection circuit and on the magnitude of the charge/discharge current. Said circuit is characterized that an arrangement of short-circuit switches comprising parallel arranged partial switches is located parallel to the charge/discharge terminals, that an overvoltage detector closes, in case of an overvoltage on charge/discharge terminals, all partial switches via a control logic, which afterwards cyclically progressing opens one partial switch after the other, and that a voltage detector, monitoring the remaining voltage over the partial switches inhibits the opening of at that time next partial switch if the remaining voltage over the still closed partial switches is higher than a predefined limit of said remaining voltage. Furthermore said control logic activates a permanent disconnection of the battery from the charge/discharge terminals if the cycle is not completed within a predefined time interval, that means if at least the last partial switch is still closed.